fix bug in p4est (don't use MPI spec if not compiling with MPI) (#12784)
fix bug in p4est (don't use MPI spec if not compiling with MPI) (#12784)


LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack